Method of bonding a zirconia member with another member

ABSTRACT

Method of bonding together two members, one of which comprises zirconia. A mixture is prepared comprising an active metallic component such as titanium, zirconium, titanium hydride, or zirconium hydride, and a brazing metallic component such as silver, copper, gold, or the like. The mixture is applied to the region of the zirconia member to be bonded. The members are placed together in a contiguous relationship in the regions to be bonded. The members are then heated to above the melting point of the mixture in a non-oxidizing environment, such as in helium. After the members are bonded, they are cooled to an annealing temperature of the zirconia, and oxygen is slowly introduced into their environment. The oxygen makes up any deficiency of oxygen in the zirconia member resulting from the bonding procedure.

United States Patent 1 91 Spielberg et 'al.

p [54 METHOD OF BONDING A ZIRCONIA MEMBER WITH ANOTHER'MEMBER [75]Inventors: David Henry Spielberg; Charles J. Levesque, both of DesPlaines, Ill.

[73] Assigneez Universal Oil Products Company,

' Des Plaines,l1l.

[22] Filed: Dec. 20,l97l

[21] Appl.No.: 210,135

[52] US. Cl. ..29/473.l, 29/487, 287/l89.365

[51] Int. Cl. .....B23k 31/02 [58] Field of Search ..29/473.1, 487;

[56] i I References Cited UNITED STATES PATENTS 2,163,408 6/1939Pulfrich ..287/l89.365 2,512,455 6/1950 Alexander ..29/473.l 2,570,24810/1951 Kelley ....287/189.365 X 2,647,218 7/1953 Sorg et al ..29/473.1UX 2,776,472 1 /1957 Mesick, .lr. ..29/473.l X 3,110,571 Alexander..29/473.1 X

[ 51 June5, 1973 FOREIGN PATENTS OR APPLICATIONS 813,829 5/1959 GreatBritain ..29/473.l

Primary Examiner-J. Spencer Overholser Assistant Examiner-Ronald J.Shore 7 Attorney-James R. Hoatson, Jr., Ronald H. Hausch and William H.Page II 57 ABSTRACT Method of bonding together two members, one of whichcomprises zirconia. A mixture is prepared comprising an active metalliccomponent such as titanium,

zirconium, titanium hydride, or zirconium hydride,

. makes up any deficiency of oxygen in the zirconia member resultingfrom the bonding procedure.

13 Claims, No Drawings 9 1 METHOD OF BONDING A ZIRCONIA MEMBER WITHANOTHER MEMBER BACKGROUND OF THE INVENTION The present invention relatesto a method of bonding together two members, one of which compriseszirconia.

Zirconia is a ceramic type of material which has found utilization inthe field of solid oxygen electrolytes. When used as an electrolyte, itgenerally must be bonded together with an electrode made of a metallicmaterial such as stainless steel, the various iron, nickel or copperalloys, zirconium, and the like.

The state of the art of bonding together a ceramic and a metal is quitevolumous. One particular technique used for bonding together a ceramicand a metal or a ceramic and another ceramic is referred to as theactive metal" technique. Reference should be made to A Survey of Ceramicto Metal Bonding" authored by G.R. Vanllouten and found in volumn 38metallic 6 (1959) of the Ceramic Bulletin. On page 303 of that articlethere is found a brief summary of the active metal film bondingtechniques used in 1959. Basically, the'techniques use titanium orzirconium or their hydrides as the bonding agent in combination with abrazing material, such as copper, silver, gold, nickelmanganese, and thelike. The mixture is put into a solution or emulsion and painted ontothe ceramic. The ceramic is then placed into a contiguous relationshipwith member. The problem arises because of the fact that the bondingtakes place in a non-oxidizing environment. The use of a non-oxidizingor protective environment prevents the metal member from oxidizing aswell as any oxygen from interferring with the bonding chemistry. Becauseof the protective environment, oxygen from the zirconia is driven off athigh temperatures (above 450 C) into the environment during the bondingoperation. If, subsequently cooled, the oxygen deficient zirconia couldnot be utilized as a efiective electrolyte. When the zirconia isreplenished with oxygen another problem arises. Zirconia has a uniquecharacteristic in that as oxygen is reintroduced into oxygen deficientzirconia it undergoes a volumetric expansion which may exceed'20 percentat very high temperatures (around 1,500 C). This expansion phenomenawill lead to structural failure of the zirconia and/or the bond betweenthe zirconia and the other member if it proceeds too rapidly or below atemperature where the other member may relieve the increasing stressesdue to this volumetric change.

SUMMARY OF THE INVENTION Thus, it is a principal object of thisinvention to provide for a method of bonding together two members, atleast one of which comprises zirconia.

More particularly, it is an object of this invention to provide for themethod of bonding together zirconia with a metal whereby the resultingzirconia is in a fully oxidized state.

According to the broad aspects of this invention after zirconia and theother member are bonded together'at a high temperature in anon-oxidizing environment, the members are held at an annealingtemperature of the zirconia. Oxygen is then introduced into theenvironment of the members at that annealing temperature and maintainedat that temperature for a period of time from about 30 minutes or' moredepending on the temperature used. Any oxygen deficiency in the zirconiaresulting from the bonding procedure is replenished without detrimentaleffects on the two members.

Initially, the zirconia is preferably bonded to the other member byfirst preparing a mixture comprising a metallic component selected fromthe group consisting of titanium, zirconium, titanium hydride, andzirconiu'm hydride, and a brazing metallic component. The mixture isapplied to the region of the zirconia member to be bonded and themembers are placed with the re gions to be bonded in contiguousrelationships. The members are then placed into a non-oxidizingenvironment and heated to above the melting temperature of the mixture.Preferably, the mixture of the active metallic component and the brazeis :a eutectic mixture of a relatively low melting point.

THE PREFERRED EMBODIMENT In a preferred embodiment of our invention aeutectic mixture comprising titanium hydride and a powdered brazingmetal, such as copper, is applied to the region of a zirconia member tobe bonded with a metal alloy member such as nickel plated zircaloy,which is a zirconium alloy. Preferably, the zircaloy is first nickelplated in the region to be bonded. The eutectic mixture chosenpreferably has a melting point of about 870 C. The hydride and brazingmetal mixture may be held in suspension in alcohol, water, resin,binder, or the like,

which is painted or sprayed on the zirconia, although a solid foil maywell be prepared from the mixture. After coating the zirconia memberwith the titanium hydride mixture, the zirconia member and the zircaloymember are held together in close contact. The members are then placedinto a pure helium atmosphere and heated to above the melting point ofthe mixture which for the eutectic titanium hydride-copper is about 870C. The hydride dissociates and prepares the surface of the zirconia fora chemical reaction with titanium. It is believed that the titaniumcomponent of the mixture bonds chemically to the zirconia and the coppercomponent brazes with the nickel coated zircaloy. After about 3 to 5minutes at this temperature, the members are cooled slowly to theannealing temperature of the zirconia. We have found that the zirconiawill anneal properly above about 450 C. Anything over 800 C will causeoxidation of the zircaloy when the oxygen is introduced into theenvironment; therefore, 650 C is chosen as an optimum temperature forthe system. The upper limit temperature will of course depend on thetype of material used. The oxygen is slowly diffused into theenvironment as atmospheric air. The oxygen diffusion may take from 5minutes or more. After about 8 hours at this annealing temperature themembers are allowed to cool to room temperature. The result is ahermetic seal of zirconia and zircaloy with oxygen restored in thezirconia.

While the present invention involves the use of titanium hydride as itspreferred embodiment, zirconium, titanium or the hydride of zirconiummay also be used alone or in combination with titanium hydride. We havefound, however, that in general the two forms of the hydrides formsuperior bonds with the zirconia. Also instead of an inert environment,it is possible to bond the members initially in a reducing environmentsuch as in a pure dry hydrogen atmosphere (except with zircaloy which isembrittled by hydrogen).

EXAMPLES Example 1 A stabilized zirconia disc was painted with atitanium hydride-copper brazing mixture suspended in water in a eutecticmixture ratio of about 28 percent titanium hydride and about 72 percentcopper by weight. The zirconia disc was comprised of zirconium dioxidestabilized with 15 mole percent calcia. A nickel plated zircaloy memberwas placed in contact with the painted surface of the zirconia. Thezircaloy member was comprised of a tubular member, whose surface wascarefully prepared and then electroless nickel plated. The two memberswere placed in a sealed oven and helium was allowed to flow through theoven. The temperature was raised in the oven to about 900 C (900 C isabove the melting temperature of the mixture 870 C) for about 3 minutesafter which it was dropped to about 650 C, an annealing temperature ofthe zirconia below which the zircaloy member would not oxidize readilyupon introduction of air. At this temperature, atmospheric airwasallowed to slowly diffuse into the oven by stopping the helium flowand opening a port to the air in order to reoxidize the zirconia. Themembers were held in equilibration with room air for hours. The resultwas a completely hermetic seal of the zircaloy and zirconia withcomplete reoxidation of the zirconia, and no detrimental effects on thebond or the zirconia upon subsequent reheating in air. Example 2 Thesame procedure of Example 1 was followed except titanium was used in theeutectic mixture instead of its hydride. Example 3 The same procedure ofExample 1 was followed with the exception that a eutectic mixture of 47percent zirconium hydride and 53 percent copper by weight and having amelting point of 890 C was applied to the zirconia disc. Again goodbonding and structural results were obtained. Example 4 The sameprocedure of Example 3 was followed except zirconium was used in theeutectic mixture instead of its hydride.

We claim as our invention:

1. Method of bonding together two members, at least one of whichcomprises zirconia, which comprises:

a. preparing a mixture consisting essentially of a metallic componentselected from the group consisting of titanium, zirconium, titaniumhydride, and zirconium hydride, and a brazing metallic component;

b. applying the mixture to the region of the zirconia member to bebonded;

c. placing the members with the regions to be bonded in contiguousrelationship;

d. heating the members to above the melting point of said mixture in anon-oxidizing environment;

e. cooling the members to an annealing temperature of said zirconia;and,

f.'introducing oxygen into the environment of said members at saidannealing temperature, whereby any oxygen deficiency in the zirconia isreplenished without detrimental effects on the two members.

2. The method of claim 1 wherein said mixture is an eutectic mixture.

3. The method of claim 1 wherein said metallic component is zirconium.

4. The method of claim 1 wherein said metallic component is titanium.

5. The method of claim 1 wherein said metallic component is zirconiumhydride.

6. The method of claim 1 wherein said metallic component is titaniumhydride.

7. The method of claim 1 wherein said members are maintained at theannealing temperature over about 4 hours.

8. The method of claim 1 wherein said brazing compound comprises copper.

9. The method of claim 1 wherein said brazing compound comprises silver.

10. In a method of bonding two members, at least one being zirconia,wherein said members are heated to above about 450 C in a non-oxidizingenvironment during the bonding procedure, the steps following theinitial heating and bonding of said members comprising:

a. holding said members at an annealing temperature of said zirconia;and,

b. introducing oxygen into the environment thereof at said annealingtemperature, whereby any oxygen deficiency in the zirconia isreplenished without detrimental effects on the two members- 11. Themethod of claim 10 wherein oxygen is introduced into the environment asatmospheric air.

12. The method of claim 10 wherein the other member is stainless steel.

13. The method of claim 10 wherein the other member is zircaloy.

4K III R III l

2. The method of claim 1 wherein said mixture is an eutectic mixture. 3.The method of claim 1 wherein said metallic component is zirconium. 4.The method of claim 1 wherein said metallic component is titanium. 5.The method of claim 1 wherein said metallic component is zirconiumhydride.
 6. The method of claim 1 wherein said metallic component istitanium hydride.
 7. The method of claim 1 wherein said members aremaintained at the annealing temperature over about 4 hours.
 8. Themethod of claim 1 wherein said brazing compound comprises copper.
 9. Themethod of claim 1 wherein said brazing compound comprises silver.
 10. Ina method of bonding two members, at least one being zirconia, whereinsaid members are heated to above about 450* C in a non-oxidizingenvironment during the bonding procedure, the steps following theinitial heating and bonding of said members comprising: a. holding saidmembers at an annealing temperature of said zirconia; and, b.introducing oxygen into the environment thereof at said annealingtemperature, whereby any oxygen deficiency in the zirconia isreplenished without detrimental effects on the two members.
 11. Themethod of claim 10 wherein oxygen is introduced into the environment asatmospheric air.
 12. The method of claim 10 wherein the other member isstainless steel.
 13. The method of claim 10 wherein the other member iszircaloy.